1. Field of the Invention
The present invention generally relates to an image drum cartridge and a developing unit.
2. Description of the Related Art
A conventional image forming apparatus such as a printer, a facsimile machine, and a copying machine incorporates a photoconductive drum (i.e., image drum). There are provided a charging roller, an exposing unit, a developing roller, a transfer roller, and a cleaning roller in this order around the photoconductive drum. The charging roller charges the surface of the photoconductive drum uniformly. The exposing unit illuminates the charged surface to form an electrostatic latent image on the photoconductive drum. The developing roller applies toner to the electrostatic latent image to develop the electrostatic latent image into a toner image. The transfer roller transfers the toner image onto a recording medium. The recording medium having the toner image thereon passes through a fixing unit where the toner image is fused into a permanent image.
Structural elements such as the photoconductive drum, charging roller, developing roller, and cleaning roller have relatively short lives. Additionally, toner is a consumable item. Thus, a recent trend is that these structural elements including a toner cartridge are integrally assembled into a unitary construction, i.e., an image drum cartridge, so that the whole assembly can be quickly replaced for a new, unused one.
FIG. 25 illustrates the positional relationship between a photoconductive drum 23 and a developing roller 24 of a conventional art.
The rotational axes of the photoconductive drum 23 and the developing roller 24 are spaced apart by a predetermined distance in such a way that the developing roller 24 is in pressure contact with the photoconductive drum 23 to create a nip D between them.
With the conventional image forming apparatus, the nip D is present between the photoconductive drum 23 the developing roller 24 even when they are at rest. The presence of the nip D at all times causes a mark of the nip D to be left on the photoconductive drum 23 or causes the surface of the developing roller 24 to deform. Thus, when a print operation is performed after a long time storage of the apparatus, lines appear in a printed image, the lines extending in a direction in which the nip D extends.